It pretty much continues what was happening within the first book. Mercy ends up falling into a mystery concerning the vampires and a demon possessed vampire bent on killing and sending out a radar of violence inducing stimuli. And of course Mercy is the perfect person to be rid of the demon vampire. With the help of Stefan and continued help from Samuel and Adam, and Adam’s pack, she takes on the beast.
And OF COURSE it ends with a cliffhanger! Both Samuel and Adam are still pursuing her to be their mates. I feel for both of them but I’m hopeful that she’ll make her choice in the next book.